Chlamydia testing urgently needs to shift its focus to the under-25s, the Scottish government has said.
Figures from the statistics division of the NHS have shown that the majority of all cases of the sexually transmitted infection (STI) occurred in people under the age of 25.
Despite this age group representing 72% of all cases of chlamydia, just 48% of tests were carried out on this age group in Scotland in 2009, the report shows.
Public health minister, Shona Robison, said: "This report shows that there is still work to be done to ensure that chlamydia testing is being targeted at those most at risk - most notably, young people under 25."
Between 2008 and 2009, a total of 267,854 people were tested for chlamydia - a small increase of 2,991 from the previous year.
The figure had risen by 20% compared with 2005, the report shows.
Statistics have also shown that the two groups with the highest proportion of samples testing positive were women aged 15-19 (12%) and men aged 20-24 (14%).
The number of positive tests was higher in men among all age groups, but the majority of tests (76%) were taken by women.
The highest proportion of positive chlamydia tests among women aged 15-24 was in NHS Ayrshire and Arran, and NHS Lanarkshire (both 12%).
The highest number among men aged 15-24 was observed in NHS Borders and NHS Dumfries and Galloway (both 18%). However, the highest proportion positive among men aged 25-49 was in NHS Forth Valley and NHS Grampian at 11%.